Northwest Instruments and Controls Inc. - Process control equipment for the states of Colorado, Montana, Wyoming and Northern New Mexico

Valve Seat Leakage Chart
The Fluids Control Institute (FCI) Standard ANSI/FCI 70.2 establishes a Valve’s allowable seat Leakage Rate. The standard recognizes five degrees of seat tightness.

ALLOWABLE SEAT LEAKAGE CLASSES Leakage Class	Maximum Seat Leakage	Test Fluid	Test Pressure	Relative Seat Tightness
Class II	0.5% of rated CV	Water	45 to 60 PSI	1.0
Class III	0.1% of rated CV	Water	45 to 60 PSI	5.0
Class IV	0.01% of rated CV	Water	45 to 60 PSI	50
Class IV+	0.0015 ml /min/inch of trim size/ ΔP(PSI)	Water	Max Operating ΔP	150,000
Class V	0.0005 ml /min/inch of trim size/ ΔP(PSI)	Water	Max Operating ΔP	300,000
Class VI	about 0.9 ml/min ∗	Air	50 PSI	600,000